DESCRIPTION. Studies on the relationship between structure and function in the Ca2+ pumping ATPase of plasma membranes will be continued. These Ca2+ pumps exist in the plasma membranes of heart, smooth muscle, kidney, brain, intestinal epithelium, erythrocyte and many other cell types. They are involved in control of intracellular Ca2+ levels in cells of all kinds, and in movement of Ca2+ across epithelial cell layers such as the intestinal and kidney tubule epithelium. Information about the regulation of these pumps may thus give information relevant to hypertension and kidney disease, among other conditions. The pump consists of a single polypeptide chain of molecular weight 127,000-137,000 (the exact molecular weight depends on the isoform). Four genes encode different isoforms, and additional forms are created by alternate splices. The applicant's laboratory has succeeded in expressing this pump on COS cells and have developed an assay system for determining the activity of the expressed enzyme. Studies are proposed to extend the present knowledge of the function of the different parts of this enzyme. The structure-function relationships will be mapped by site-directed mutagenesis (utilizing the COS cell system). The properties of the isoforms will be determined which will hep to define the role of the different forms. Antibodies will be developed to identify the isoforms expressed in different cell types.